Method for laterally-coupling frequency-converted laser radiation out of a resonator

Abstract

In traveling-wave ring-resonator an optically nonlinear crystal for converting visible radiation to ultraviolet (UV) radiation has an input face and two output faces. The visible light propagates through the crystal from the input face to one of the output faces. That output face is coated with a dichroic optical coating that transmits unconverted visible light and reflects the ultraviolet light. The reflected ultraviolet light exits the optically nonlinear crystal via the other output face and is coupled out of the resonator at an angle to the resonator axis.

1. Optical apparatus comprising:
 an optical resonator having a resonator axis and arranged to cause a beam of optical radiation having a first-wavelength to circulate therein in one direction only along said resonator axis; and 
 an optically nonlinear crystal located in said optical resonator on said resonator axis, said optically nonlinear crystal being arranged to convert said circulating first-wavelength wavelength radiation to optical radiation having a second wavelength shorter than said first-wavelength, and to reflectively couple said second-wavelength radiation out of said resonator at an angle to said resonator axis and wherein said optically nonlinear crystal has an input-face, and first and second output-faces and is arranged such that said circulating first wavelength radiation enters said crystal via said input face thereof and exits said optically nonlinear crystal via said first output face thereof, and such that said second-wavelength radiation is coupled out of said resonator via said second output face of said optically nonlinear crystal. 
 
   
   
     2. The apparatus of  claim 1 , wherein said input face and said first output face of said optically nonlinear crystal are arranged such that circulating first-wavelength radiation is incident on said input face at about the Brewster angle and exits said first output face at about Brewster-angle incidence thereto. 
   
   
     3. The apparatus of  claim 1 , wherein said second-wavelength radiation is incident on said second output face of said optically nonlinear crystal at about the Brewster angle. 
   
   
     4. The apparatus of  claim 1 , wherein said second output face of said optically nonlinear crystal is inclined such that said second-wavelength radiation is incident thereon at the Brewster angle in a first plane, and incident normally thereon in a second plane perpendicular to said first plane. 
   
   
     5. Apparatus of  claim 1 , wherein said second output face of said optically nonlinear crystal is inclined such that said second-wavelength radiation is incident thereon about normally in any two mutually perpendicular planes. 
   
   
     6. The optically nonlinear crystal of  claim 5 , wherein said second output face has an antireflection coating thereon said antireflection coating arranged to minimize reflection of unpolarized second-wavelength radiation. 
   
   
     7. The apparatus of  claim 1 , wherein said first wavelength is twice said second wavelength. 
   
   
     8. The apparatus of  claim 1 , wherein said optical resonator is a passive resonator formed by a plurality of mirrors and said optical resonator is configured such that first-wavelength radiation can be injected into said resonator via one of said plurality of mirrors to provide said circulating first-wavelength radiation. 
   
   
     9. The apparatus of  claim 8 , wherein said resonator is formed by two plane mirrors and two convex mirrors, wherein said optically nonlinear crystal is located between said convex mirrors, and wherein said first-wavelength radiation is injected into said resonator via one of said plane mirrors. 
   
   
     10. Optical apparatus comprising:
 an optical resonator having a resonator axis and arranged to cause a beam of optical radiation having a first-wavelength to circulate therein in one direction only along said resonator axis; and 
 an optically nonlinear crystal located in said optical resonator on said resonator axis, said crystal being arranged to convert said circulating first-wavelength wavelength radiation to optical radiation having a second wavelength shorter than said first-wavelength, and to reflectively couple said second-wavelength radiation out of said resonator at an angle to said resonator axis and wherein said crystal has an input-face, and first and second output-faces, and wherein said first output face includes an optical coating being transmissive for the first wavelength and reflective for the second wavelength and wherein said faces are arranged so that said circulating first wavelength radiation enters said crystal via said input face thereof and exits said crystal via the coating on said first output face thereof, and such that said second-wavelength radiation is coupled out of said resonator via said second output face after being reflected by said coating on the first output face. 
 
   
   
     11. The apparatus of  claim 10 , wherein said input face and said first output face of said optically nonlinear crystal are arranged such that circulating first-wavelength radiation is incident on said input face at about the Brewster angle and exits said first output face at about Brewster-angle incidence thereto. 
   
   
     12. The apparatus of  claim 10 , wherein said second-wavelength radiation is incident on said second output face of said optically nonlinear crystal at about the Brewster angle. 
   
   
     13. The apparatus of  claim 10 , wherein said second output face of said optically nonlinear crystal is inclined such that said second-wavelength radiation is incident thereon at the Brewster angle in a first plane, and incident normally thereon in a second plane perpendicular to said first plane. 
   
   
     14. Apparatus of  claim 10 , wherein said second output face of said optically nonlinear crystal is inclined such that said second-wavelength radiation is incident thereon about normally in any two mutually perpendicular planes. 
   
   
     15. The optically nonlinear crystal of  claim 14 , wherein said second output face has an antireflection coating thereon said antireflection coating arranged to minimize reflection of unpolarized second-wavelength radiation. 
   
   
     16. The apparatus of  claim 10 , wherein said first wavelength is twice said second wavelength. 
   
   
     17. The apparatus of  claim 10 , wherein said optical resonator is a passive resonator formed by a plurality of mirrors and said optical resonator is configured such that first-wavelength radiation can be injected into said resonator via one of said plurality of mirrors to provide said circulating first-wavelength radiation. 
   
   
     18. The apparatus of  claim 17 , wherein said resonator is formed by two plane mirrors and two convex mirrors, wherein said optically nonlinear crystal is located between said convex mirrors, and wherein said first-wavelength radiation is injected into said resonator via one of said plane mirrors. 
   
   
     19. Optical apparatus comprising:
 an optical resonator having a resonator axis and arranged to cause a beam of optical radiation having a first-wavelength to circulate therein in one direction only along said resonator axis; and 
 an optically nonlinear crystal located in said optical resonator on said resonator axis, said optically nonlinear crystal being arranged to convert said circulating first-wavelength wavelength radiation to optical radiation having a second wavelength shorter than said first-wavelength, and to reflectively couple said second-wavelength radiation out of said resonator at an angle to said resonator axis and wherein said optical resonator is a passive resonator formed by a plurality of mirrors and said optical resonator is configured such that first-wavelength radiation can be injected into said resonator via one of said plurality of mirrors to provide said circulating first-wavelength radiation and wherein said resonator is formed by two plane mirrors and two convex mirrors, wherein said optically nonlinear crystal is located between said convex mirrors, and wherein said first-wavelength radiation is injected into said resonator via one of said plane mirrors.